Protein A-bearing strains of Staphlococcus aureus contain a cell wall polypeptide that binds to the Fc region of many mammalian IgG subclasses and has a high affinity for immune complexes. Recently it has been reported that use of such bacteria in an extracorporeal blood processing technique results in tumor regression in canine mammary adenocarcinoma (Terman et al, The Journal of Immunology, 124, 795-805 (1980)) and reversal of feline leukemia when the technique is used in combination with low dose irradiation (Jones et al., Cancer, 46, 675-684 (1980)).
The blood processing technique involves withdrawing a portion of the total blood volume of the tumor bearing host, separating the blood into plasma and formed elements by centrifugation, running the separated plasma through a biological filter containing heat-killed and formalin-fixed protein A-bearing Staphlococcus aureus, and thereafter recombining the treated plasma and formed elements into whole blood which is returned to the host subject.
Although the mechanism of the tumor regressions reported remains unclear, it has been established that serum IgG levels in treated subjects decline immediately after perfusion of the plasma over the bacteria and then rebound above preperfusion levels. Regardless of the mechanism(s) involved, the ex vivo removal of serum IgG and immune complexes appears to be a key factor in the observed clinical improvement in the subjects studied.
The disadvantage of the prior art blood processing technique is that it requires separation of plasma from formed elements prior to perfusion of the plasma. Such a separation step is not only time consuming but also increases the possibility of contamination which could be critical to the treated subject.
It has now been discovered that IgG and immune comlexes can be removed from whole blood thereby eliminating the need to separate the blood into formed elements and plasma prior to removal of the substances from the plasma.